The present invention relates to injection molding equipment and more particularly to equipment for measuring pressure in a mold cavity during injection of molded parts.
Injection molding processes generally involve the injection of a liquid material into a mold cavity for curing. The resulting molded article must be removed, or ejected, from the opened mold after curing. The equipment for removing molded articles from a mold is referred to as the ejector assembly. Often, the ejector assembly includes ejector pins which are retracted during molding and are extended during ejection to force the article from the opened mold. In the case of concave molded parts formed over a core pin, the ejector assembly includes a sleeve encircling and riding along the core. The sleeve is retracted during molding and is extended during ejection to ride along the core and force the article off the core pin.
In order to achieve the highest quality finished parts, the liquid material must be injected into the mold cavity at the proper pressure. In extreme instances, insufficient pressure may lead to porous, pitted or incomplete parts. On the other hand, excessive pressure may damage the molding apparatus or result in seam lines along mating portions of the mold halves. Under normal processing conditions, part dimensions, strength, and general quality are dependant upon consistent mold pressure.
A prior technique for measuring the pressure within a mold cavity during injection uses a flush-mount style transducer, such as a strain gauge or peizoelectric type transducer. The transducer is mounted directly on the interior surface of the mold cavity in contact with the part to measure the cavity pressure. When mounted on a cosmetic surface of the mold cavity, the transducer leaves an undesired mark on the surface of the article. Secondly, many molds do not lend themselves well to the installation of a flush-mount style transducer. For example, the mold may include obstructions or the transducer may interfere with proper functioning of the mold.